The psychoactive compound (+)-3,4-methylenedioxymethamphetamine (MDMA) is a common drug of abuse popularly known as "ecstasy". There is a segment of the therapeutic community who claim MDMA may be a useful therapeutic tool because it promotes empathy and communication. However, MDMA is currently a Schedule I compound, making any medical use of it illegal. Moreover, it is likely that MDMA possesses neurotoxic properties. The psychoactive effects of MDMA are thought to be mediated through dopamine and serotonin neurotransmitter systems. MDMA is classified as both a "stimulant" and a "hallucinogen" because it shares subjective and physiological properties of both classes. We have established that the discriminative stimulus effects of MDMA can be differentiated by rats from those produced by the dopaminergically-mediated amphetamine cue. Thus, the specific aim of the present research proposal is to use a complex drug discrimination procedure to determine if the stimulus properties of MDMA can be differentiated from those of the serotonergically- mediated LSD cue. Twenty-four rats will be trained using a fixed-ratio 10 (FR 10) schedule of food reinforcement. Additionally, because drug discrimination research is time consuming, differential outcomes will be implemented to ascertain if this procedure facilitates the acquisition of the discrimination and/or the terminal accuracy of the acquired response. Differential outcomes will consist of pairing an exterioceptive stimulus (i.e., a light or tone) with each interioceptive stimulus condition (i.e., MDMA, LSD, or saline). The tone/light will be presented concurrently with the delivery of reinforcement. A control group will be exposed to these pairings on a random basis. Overall, it is important to accurately classify compounds with respect to abuse liability in order to identify and provide the most beneficial treatments; and in the case of MDMA, to evaluate therapeutic potential.